Airless spray gun with variable output



Aug. 3, 1965 J. H. MGNINCH, JR, ETAL 3,193,439

AIRLESS SPRAY GUN WITH VARIABLE OUTPUT Filed May 10, 1963 2 Sheets-Sheet1 Fag L7.

INVENTOR. Josa u H. McNman J! gygzrr J. DELLA F'Lmu AT? 02 Ni-YS Aug. 3,1965 J. H. MONINCH, JR.. ETAL 3,198,439

AIRLESS SPRAY GUN WITH VARIABLE OUTPUT JOSEPH H. McNmca J2. OBER'T J.DELLA FLou QMW A TORNEYS United States Patent 3,198,439 AIRLES gPRAY GUNWITH VARIABJE ()UTEUT Joseph H. McNinch, IL, and Rohert J. Della Flora,To-

ledo, Ohio, assignors to The De Vilhiss Qompany, Toledo, Ohio, acorporation of llhio Filed May 16, 1963, Ser. No. 279, :3l 13 Claims.(l. 239-332) This invention relates to spray gun which utilizes lowpressure coating material, raises its pressure, and ejects it as anairless spray, and more particularly to an improved means for varyingthe .coating material output of such a spray gun.

Spray guns capable of airless atomization of coating material providegood control of the coating material and substantially reduce overspray.With airless spray guns heretofore known, however, the coating materialis placed under high pressure by means of a pump or other device locatedat some distance from the spray gun. Consequently, the pump, hose, andother components of the system between the pump and the spray guncontain coating material at high pressure. These components, therefore,must be of heavy, expensive construction to safely contain the highpressure coating liquid.

The spray gun according to the present invention atomizes coatingmaterial by means of high pressure and without air, but employs coatingmaterial from a relatively low pressure source and increases thepressure only after the material has entered the spray gun.Consequently, only an ordinary low pressure source, hose, and relatedcomponents are required for the coating system.

The pressure of the coating material is raised within the new spray gunby means of air or other suitable power fluid which itself is only atmoderate pressure and can be supplied to the spray gun from aconventional a-ir compressor. The relatively low pressure power fluidraises the pressure of the relatively low pressure coating material bymeans of a reciprocating piston assembly which includes a large diameterpower piston and a small diameter coating material piston to achieve thedesired pressure rise. The coating material is then ejected or sprayedin rapid pulses which provide a substantially continuous flow ofatomized coating particles. The new spray gun in particular employsimproved means for varying the coating material output more effectivelythan heretofore and accomplishes this by changing the stroke length ofthe power piston. The quantity of coating material sprayed thus can bechanged in the new spray gun even though the pressure of the power fluidremains constant. Further, the length of the stroke can be changed bymeans 'of a simple adjusting member easily controlled by the operator.The new spray gun also has more effective means for controlling thecoating material pressure than heretofore.

It is, therefore, a principal object of the invention to provide anairless spray gun of the type described which has improved means foradjusting the coating material output and for controlling coatingmaterial pressure.

Other objects and advantages of the invention will be apparent from thefollowing detailed description of a preferred embodiment thereof,reference being made to the accompanying drawing, in which:

FIG. 1 is a schematic view in elevation of a spray gun and supplyequipment embodying the invention;

FIG. 2 is an enlarged, fragmentary view in longitudinal cross section ofthe spray gunslrown in FIG. 1; and

FIG. 3 is a view in cross section taken along the line 3-3 of FIG. 2.

Referring to the drawings, and more'particularly to FIG. 1, a spray gunembodying the inventionis indicated 3398,43? Patented Aug. 3, 19%?) atit) and includes, a main body 12, a handle 14, and a relatively lowpressure by air supplied through a line 24 from a storage tank 26 and acompressor 28.

Coating material under relatively low pressure is supplied to the spraygun 10 from the line 20 through a sup- .ply passage 3% (FIG. 2) and anannular manifold 32. A

plurality of valve passages 34 communicate with the annular manifold 32and also with a coating material chamber or cylinder extension 36 andacoating material cylinder 38. The valve passages 34 normally areblocked by .a check valve ring 40 which .is-urged against the ends ofthe passages 34 by means of a spring 42. The passages 34, the ring 49,and the spring 42 constitute check valve means which enable'coatingmaterial to enter the chan1 ber 36 from the supply opening 30 but not toflow in the reverse direction.

A coating material piston 44 to raise the pressure of the coatingmaterial extends through the coating material cylinder 38 and into thechamber 36. When the piston 44 is retracted, by means to be discussedsubsequently, the pressure in the cylinder 38 and the chamber 36 isreduced, enabling the coating material in the manifold 32, which isunder some-pressure,to overcome the force of the spring 42 and open thevalve ring 49. With the coating material chamber 36 filled, when thepiston 44 moves forwardly again, the coating material is placed under.rapidly increasing pressure and must eventually be able to escape fromthe chamber 36. For this purpose, a group of outlet passages 46 arelocated at a forward end of the chamber 36 and communicate with acentral outlet passage 45 in an outlet valve member 50. Coating materialflow to the passage 4% depends on the position of the outlet valvemember 50 which can be seated near the group of outlet passages 46 toprevent flow or can be moved forwardly by the coating material pressureto permit flow. A suitable seal 52 prevents" leakage of coating materialoutside the valve memberSll. V

The valve member 50 normally is held against the seat adjacent theoutlet passages 46 by means of power fluid pressure in a pressurecylinder 54 which acts on a valve piston 56. The power fluid is suppliedto the cylinder 54 by a supply passage 58 in the end of the spray gun10, which passage is connected by any suitable tube or passage means 60to a power fluid supply passage 62 in the handle 14 upstream of a powerfluid valve V operated by the trigger 16. The passage 62 communicateswith the supply line v18. The power fluid pressure in the cylinder 54holds the valve member 50 against its seat until the force of thepressurized coating material acting upon the end of the member 50exceeds the force of the power fluid on the piston56, whereupon themember 50 will move quickly away from the seat and enable coatingmaterial to-flow from the outlet passages 46 through the passage 48 andto a suitable nozzle cap 64. The nozzle of the cap 64 can be' designedin accordance with high pressure spray nozzles known in the art and doesnot constitute a novel part of the present invention. The'rear of thepressure cylinder 54 is suitably vented through a vent passage 65.

The force of the air or other power fluid acting on the piston 56 of thevalve member 50 not only determines the pressure which the coatingmaterial in the chamber 36 must reach before being sprayed from the gun10, but also determines the cut-off pressure, below which no coatingmaterial will issue from the gun. In this manner, spattering or randomflow of poorly atomized coating material particles is substantiallyeliminated, thereby eliminating a problem common to high pressurecoating material spray guns heretofore known. The piston and cylinderarrangement also causes the valve member 50 to open at a givenpercentage of operating pressure, regardless of the amount of thepressure. A wide range of pressure thus can be used while maintaining ahigh cut-oft pressure.

From the above operation, it will be apparent that the coating materialis supplied to the nozzle cap 64 in pulses, one during eachreciprocatory cycle of the coating mateterial piston 44. These pulsesare so frequent, however, that they establish a substantially continuousspray when the trigger 16 is pulled. The off time of the spray gun,namely that time in which the coating material is not being discharged,will determine the gaps between the individual sprays emitted from thenozzle, and this oif time should be uniform and held to a minimum. Inpractice, the piston 44 preferably reciprocates at a rate of 2000 to6000 times per minute, which provides from 2000 to 6000 pulses or spraypatterns per minute. From a practical standpoint, this almostconstitutes a continuous spray.

The operating mechanism for the coating material piston 44 will now beexplained. The piston 44 is connected through an intermediate, enlargedmember or stem 66 to a power piston 68 so that the power piston 68 andthe coating piston 44 are functionally integral. The power piston 68 islocated in a power cylinder 70 formed by a cylindrical wall 72 in therear of the gun 10. A spring chamber 74 opens into the cylinder 70 andholds a return spring 76 which is compressed between an end of thechamber 74 and the forward side of the piston 68, thereby urging thepiston 68, the stem 66, and the coating material piston 44 toward rearpositions. spring 76 provides a simple means for returning the pistonand preferably has a small preload so that the piston will be returnedin a constant amount of time regardless of the length of stroke. In thismanner, the off time will be relatively constant under all conditions.

The piston 68 is moved forwardly against the force of the spring 76 bythe pressure of the power fluid supplied through the line 18 and thepassage 62. This fluid is admitted through a power fluid inlet '78 to anannular fluid supply manifold 80. From the manifold, the power fluid canflow through four flow control openings 82 (FIG. 3) in an annular valveplate 84, the openings being formed by notches or flat peripheralportions in the plate 84. Unless the valve plate 84 is against a supplyvalve seat 86 formed at the end of the cylinder wall 72, the power fluidI will then fill the rear end of the power cylinder 70, overcoming theforce of the spring 76 and moving the power piston 68 forwardly in thecylinder 70, thereby similarly movingthe coatingmaterial piston 44. Asthe high pressure fluid fills the power cylinder 70, it also passesthrough minute valve passages 88 and into a power fluid valve chamber90, with this power fluid. then tending to urge the valve plate 84against the seat 86. This pressure, however, will be more than offset bythe pressure in the cylinder 70, until the pressure in the cylinder 70drops substantially. Hence,,until the pressure drops, the valve plate 84will remain away from the seat 86 and power fluid can continue to enterthe cylinder 70.

A cylindrical exhaust projection 92 extends rearwardly from the piston68 and moves therewith. The projection 92 cooperates with a cylindricalexhaust opening or port 94 in a threaded stroke control member 96. Theprojection 92 blocks and closes off the opening 94 during most of thetravel or stroke of the piston 68, until the piston 68 reaches aposition near the forward end of its stroke.

'At that time, the projection 92 moves out of the opening 94, as shown,to enable the high pressure power fluid in the rear end of the cylinder70 to escape through the control member 96. The pressure of the fluid inthe valve chamber 90 and in the manifold 80 then forces the valve plate84 forwardly against the seat 86 to prevent further entry of highpressure fluid into the cylinder 70. With the sudden drop of pressure inthe rear end of the cylin- The return 7 4 turn stroke. During this time,fluid in the chamber 90 blee 3 through the holes 88 so that pressure inthe chamber 90 is substantially at atmospheric by the time the piston 68completes its return stroke. As the piston 68 moves rearwardly, theprojection 92 again closes the exhaust port 94, but, with the valveplate 82 in the forward position against the supply valve seat 86,exhaust passages 98 are opened, with the valve plate 84 having movedaway from an annular exhaust valve seat 100. Remaining power fiuid inthe cylinder 70 can then exhaust through the passages 98 to rear vents102. When the piston 68 approaches the rear end of the cylinder 70adjacent the vaive plate 84, an exhaust control shoulder 104 adjacentthe piston 68 cooperates with the inner diameter of the valve plate 84to block further flow of power fluid from the cylinder 70 through theexhaust passages 98. Thus, the remaining fluid is trapped between thepiston 68 and the valve plate 84 to act as a cushion for the end of thestroke of the piston 68 and also to force the valve plate 84 rearwardlyagain, away from the supply valve seat 86 and against. the exhaustpassage seat 100. Pressurized power fluid is then again admitted betweenthe valve plate. 84 and the seat 86 to the cylinder 70 to. again drivethe piston 68 forwardly.

The operator can adjust the stroke, of the piston 68 by turning thestroke control member 96 toward or away from the cylinder '70 and theexhaust projection 92. By screwing the member 96 into the spray gun body12 and toward the cylinder 70, the operator can increase the length ofstroke of the piston 68. The exhaust opening 94 is thus moved toward thecylinder 70 and the exhaust projection 92 does not uncover the opening94 until the piston 68 moves farther toward the front end of the spraygun. The length of the stroke thereby is increased since the oppositeend of the stroke always remains at the same point, adjacent the valveplate 84.

The operator can also screw the member 96 out of the gun body and awayfrom the cylinder 70 to similarly move the exhaust opening 94, wherebythe exhaust projection 92 will move out of the opening sooner and enablethe escape of pressurized fluid from the rear of the cylinder 70 earlierthan otherwise. The fluid is thereby exhausted sooner and the length ofthe stroke of the piston 68 is correspondingly shortened.

in each case that the stroke of the power piston 68 is lengthened orshortened, the stroke of the coating material piston 44 iscorrespondingly lengthened or shortened thereby to increase or decreasethe amount of coating material sprayed from the gun upon each completecycleof the piston 68.

While the overall operation of the spray gun should be apparent from theabove description, it will be reviewed for the sake of clarity. Whenspraying is to begin, air or other power fluid from the tank 26 issupplied to the source 22 to place the coating material therein undersome pressure. The material, under a pressure of 100 pounds per squareinch, for example, is then fed through the line to the inlet passage andthe manifold 32. At the same time, the power fluid is supplied throughthe line 18 and the supply passage 62 to the manifold 80. The fluid alsois supplied through the passage to the inlet passage 58 and the chamber54.

The fluid in the annular manifold 80 passes between the valve plate 84and the valve seat 86 and into the rear end of the power cylinderthereby moving the piston 68 forwardly against the force of the spring76. As this movement occurs, the exhaust projection 92 also moves withthe piston 68. Movement continues until the projection 92 is out of theopening, at which time the pressurized power fluid in the rear of thecylinder 70 is exhausted through the opening 94, this fluid beingexhausted much faster than it can be admitted to the cylinder throughthe openings 82 of the valve plate 84. Pressure of fluid in the chambersand then forces the valve plate 88 to move forwardly and engage thevalve seat 86 to prethen predominates to move the piston 68 toward therear.

At this time, the valve plate 84 continues to be held in its forwardposition against the seat 86 mainly because of the force of the powerfluid in the chamber 80 so that the fluid in the cylinder 70 can exhaustthrough the vent passages 98. When the shoulder 104 cooperates with theinner edge of the valve plate 84, the remaining fluid in the rear of thecylinder 70 is trapped, which helps the piston 68 to reverse directionand also forces the valve plate 84 to the rear position, overcoming theforce of the fluid in the chamber 80. Once again, fluid can flow throughthe openings 82 between the valve plate 84 and the seat 86 to startanother forward stroke of the piston 68.

During the return stroke of the piston 68, the coating material piston44 moves rearwardly to tend to establish a negative pressure in thecoating material chamber 36. The pressure differential across the checkvalve plate 40 is then suflicient to overcome the relatively light forceof the spring 42 and move the valve plate 40 away from the passages 34.Coating material then flows from the annular manifold 32 into thechamber 36 and the cylinder 38 until the piston 44 reaches the rear endof its stroke. As the coating material piston 44 again moves forwardlyalong with the power piston 68, the coating material pressure in thechamber 36 rises until the force of the coating material acting on thevalve member 50 overcomes the force of the power fluid in the chamber 54acting on the piston portion 56 of the valve member 50. The valve member50 then moves away from its seat to enable coating material in thecentral outlet chamber 48 to move into the passage 52 and be supplied tothe nozzle cap 64. By way of example, the force of the power fluid onthe piston 56 of the valve member 50 keeps the valve member closed untilthe coating material pressure exceeds 80% of the desired pressure forthe coating material. The outlet pressure remains the same even thoughthe length of the piston stroke is shortened or lengthened and theoutput of the gun can be varied while maintaining the pressure of thepower fluid constant.

Various modifications of the above described embodiment will be apparentto those skilled in the art, and it is to be understood that suchmodifications can be made without departing from the scope of theinvention, it they are within the spirit of the depending claims.

We claim:

1. An airless spray gun comprising a spray gun body, means forming apower cylinder, a power piston located in said power cylinder, passagemeans in said spray gun body connected to a rear portion of said powercylinder, means for supplying power fluid to said passage means, fluidvalve means to regulate flow of power fluid to said power cylinder, rearexhaust port means in said body communicating with the rear portion ofsaid power cylinder, exhaust valve means for opening and closing saidrear exhaust port means, and additional exhaust means for the rearportion of said power cylinder and opened when said power piston travelsforwardly a predetermined distance in said power cylinder.

2. A power unit according to claim 1 characterized by means foradjusting said additional exhaust means to change the predetermineddistance at which said additional exhaust means will exhaust power fluidfrom said power cylinder, thereby changing the length of stroke or saidpiston.

3. An airless spray gun comprising a spray gun body having a powercylinder, a power piston located in said power cylinder, coatingmaterial spray means including coating material pressurizing meanslocated outside said power cylinder, means connecting said powercylinder to said pressurizing means, passage means in said spray gunbody connected to the rear portion of said power cylinder, means forsupplying power fluid to said passage 6 means, fluid valve meansassociatedwith said passage means to regulate flow of power fluid tosaid power cylinder, rear exhaust port means in said body communicatingwith the rear portion of said power cylinder, exhaust valve means foropening and closing said rear exhaust port means, additional exhaustmeans for said power cylinder and opened when said power piston travelsforwardly a predetermined distance in said power cylinder, means foradjusting said additional exhaust means to change the predetermineddistance at which the exhaust means will exhaust power fluid from saidpower cylinder, thereby changing the length of stroke of said powerpiston, and means for controlling said fluid valve means to control thesupply of power fluid to said power cylinder.

4. An airless spray gun comprising a spray gun body having a powercylinder, 21 power piston located in said power cylinder, coatingmaterial spray means including coating material pressurizingmeanslocated outside said power cylinder, stem means extending throughan end wall of a front end of said power cylinder and-connecting saidpower piston to a portion of said pressurizingrneans, passage means insaid spray gun body connected to the rear end of said power cylinder,means for supplying power fluid to said passage means, valve meansassociated with said passage means for controlling the flow of powerfluid from said passage means to said power cylinder, said valve meansbeing opened when said piston is near the rear end of said cylinder,rear exhaust passage means in said body located near the rear end ofsaid power cylinder, second valve means located in said exhaust passagemeans and being open when said power piston is moving in a rearwarddirection, additional exhaust means effective to exhaust power fluidfrom said power cylinder when said power piston has moved forwardly insaid cylinder a predetermined distance, and means for adjusting theposition of said additional exhaust means to change the predetermineddistance atwhich the exhaust means will exhaust power fluidfrom saidpower cylinder, thereby changing the length of stroke of said powercylinder.

5. An airless spray gun comprising a spray gun body having a powercylinder, a power piston located in said power cylinder, coatingmaterial spray means including coating material pressurizing meanslocated outside said power cylinder, stern means extending through anend wall of a front end of said power cylinder and connecting said powerpiston to a portion of said pressurizing means, said stern means passingthrough an intermediate chamber formed by said gun body beyond the endwall of said power cylinder, resilient means in said intermediatechamber urging said power piston toward the rear, passage means in saidspray gun body connected to the rear end of said power cylinder, meansfor supplying power fluid to said passage means, valve means associatedwith said passage means for controlling the flow of power fluid fromsaid passage means to said power cylinder, said valve means being openedwhen said piston is near the rear end of said cylinder, rear exhaustpassage means in said body located near the rear end of said powercylinder, second valve means located in said exhaust passage means andbeing open when said power piston is moving in a rearward direction, anexhaust projection functionally integral with said power piston andextending rearwardly therefrom, means forming an exhaust openingcommunieating with said power cylinder beyond the rear end of a travelof said power piston, said projection extending through and blockingsaid exhaust opening throughout most of the travel of said power pistonand being out of said exhaust opening at a forward portion of the travelof said power piston to exhaust power fluid from a rear portion of saidpower cylinder, and means for adjusting the position of said exhaustopening means in a direction parallel to the direction of travel of saidpower piston-to adjust the length of travel of said power piston. v

6; An airless spray gun comprising a spray gun body having a powercylinder, a power piston located in said power cylinder, coatingmaterial spray means including coating material pressurizing meanslocated outside said power cylinder, means connecting said power pistonto a portion of said pressurizing means, valve means at a rear end ofsaid power cylinder opposite said pressurizing means, passage means insaid spray gun body connected to the rear end of said power cylinder,means for supplying power fluid to said passage means, means forming avalve seat associated with said passage means and positioned to beengaged by said valve means to prevent flow of power fluid into saidpower cylinder from said passage means, means effective to urge saidvalve means toward said first valve seat, a rear exhaust port in saidbody located near the rear end of said power cylinder, a rear exhaustpassage communicating with said exhaust port, means forming anadditional valve seat positioned to be engaged by said valve means andto close said rear exhaust passage, an exhaust projection functionallyintegral with said power piston and extending rearwardly therefrom,means forming an exhaust opening communieating with said power cylinderbeyond the rear end of the travel of said power piston, said projectionextending through and blocking said exhaust opening through most 'of thetravel of said power piston and being out of said exhaust opening at aforward portion of the travel of said power piston to exhaust powerfluid in said power cylinder through said exhaust opening, and triggermeans for controlling the supply of power fluid to said passage means.

7. An airless spray gun comprising a spray gun body having a powercylinder, a power piston located in said power cylinder, coatingmaterial spray means including coating material pressurizing meanslocated outside said power cylinder, means extending through an end wallof a front end of said power cylinder and connecting said power pistonto a portion of said pressurizing means, a valve plate at a rear portionof said power cylinder opposite the end wall, passage means in saidspray gun body connected to the rear portion of said power cylinder,means for supplying power fluid to said passage means, means forming avalve seat associated with said passage means and positioned to beengaged by said valve plate to prevent the flow of power fluid into saidpower cylinder from said passage means, means efiective to urge saidvalve plate toward said valve seat, a rear exhaust passage in said bodycommunicating with the rear end of said power cylinder and effective toexhaust power fluid between said valve plate and said power piston whensaid power piston moves in a rearward direction, means forming anadditional valve seat positioned to close said rear exhaust passage whencontacted by said valve plate, an exhaust projection functionallyintegral with said power piston and extending rearwardly thereform,means foring an exhaust opening communicating with said power cylinderbeyond the rear end of the travel of said power piston, said projectionextending through and blocking :said exhaust opening through most of thetravel of said power piston and being out of said exhaust opening at .aforward portion of the travel of said power piston to exhaust powerfluid in said power cylinder through said exhaust opening, means locatedoutside said cylinder 1 eyond said end wall and cooperating with saidconnecting means between said piston and said pressurizing means to urgesaid piston toward the rear end of said power cylinder, and triggermeans for controlling the supply of power fluid to said passage means.

8. A airless spray gun comprising a spray gun body having a coatingmaterial chamber, a coating material piston reciprocable in saidchamber, power means connected to said piston for reciprocating thesame, a coating material supply passage communicating with said coatingmaterial chamber, check valve means enabling the flow of coatingmaterial from said supply passage to said coating material chamber andblocking the flow of coating material in thereverse direction, nozzlemeans spaced from said chamber, outlet passage means connecting saidchamber and said nozzle means, pressure means preventing the flow ofcoating material from said chamber to said nozzle ,means through saidoutlet passage means when the pressure of coating material in saidchamber is below a predetermined amount, said pressure means enablingthe'flow of coating material from said chamber to said nozzle means whenthe pressure of the coating material exceeds the predetermined amount,said pressure means including a valve member in said outlet passagemeans and communicating with said coating material chamber so as to beurged toward an open position by coating material in said chamber, meansforming a power fluid chamber communicating with a portion of said valvemember, and means for supplying power to said chamber to act on saidpressure valve member and urge it toward a closed position, wherebycoating material cannot flow to said nozzle means until the force of thecoating material acting on said valve member overcomes the force of thepower fluid in said power fluid chamber acting on said valve member.

9. An airless spray gun comprising a spray gun body having a coatingmaterial chamber, a coating material piston reciprocable in saidchamber, power means connected to said piston for reciprocating thesame, coating material supply means communicating with said coatingmaterial chamber, check valve means enabling the flow of coatingmaterial from said supply means into said coating material chamber andblocking the flow of coating material in the reverse direction, anout-let port in said body communicating with said coating materialchamber, nozzle means conected with said outlet port, a pressure valvemember between said outlet port and said nozzle means and controllingflow of coating material to said nozzle means, said pressure membercommunicating with said chamber and positioned to be urged toward anopen position by the pressure of coating material in' said chamber,means forming a power fluid chamber communicating with a portion of saidvalve member, means for supplying power fluid to said power fluidchamber to act on said pressure valve member and urge it toward a closedposition, whereby coating material cannot flow to said nozzle meansexcept under high pressure.

10. An airless spray gun comprising a spray gun body having therein apower cylinder and a coating material cylinder, a coating materialpiston in said coating material cylinder, a power piston in said powercylinder and having means connecting said power piston to said coatingmaterial piston, a valve plate at a rear portion of said power cylinderopposite the coating material cylinder, passage means in said spray gunbody connected to the rear end of said power cylinder, means forsupplying power fluid to said passage means, means forming a fluidcontrol valve seat associated with said passage means and positioned tobe engaged by said valve plate to prevent the flow of power fluid intosaid power cylinder from said passage means, means effective to urgesaid valve plate toward said first valve seat, a rear exhaust passage insaid body communicating with the rear end of said power cylinder andeffective to exhaust power fluid between said valve plate and said powerpiston when said power piston moves in a rearward direction, meansforming an exhaust valve seat positioned to block said rear exhaustpassage when contacted by said valve plate, an exhaust projectionfunctionally integral with said power piston and extending rearwardlytherefrom, means forming an exhaust opening communicating with saidpower cylinder beyond the rear end of the stroke of said power piston,said projection extending through and blocking said exhaust openingthroughout the majority of the travel of said power piston to preventthe escape of power fluid from said power cylinder through said exhaustopening, means located outside said power cylinder cooperating with saidconnecting means between said power piston and said coating materialpiston to urge said power piston toward the rear of said power cylinder,coating material supply means communicating with said coating materialcylinder, check valve means enabling the flow of coating material fromsaid coating material supply means into said coating material cylinderand blocking the flow of coating material in the reverse direction, anoutlet port in said body communicating with said coating materialcylinder, nozzle means connected with said outlet port, a pressure valvemember blocking said outlet port, means urging said pressure valvemember toward the blocking position, said urging means being yieldableto enable said pressure valve member to move to an open position whenpressure of the coating material Within said coating material cylinderrises above a predetermined amount, whereby coating material can flow tosaid nozzle means under high pressure.

11. An airless spray gun comprising a spray gun body, means forming apower cylinder in said body, a power piston located in said powercylinder, passage means in said spray gun body connected to a rearportion of said power cylinder, means for supplying power fluid to saidpassage means, a supply valve plate, means forming a supply valve seateffective with said supply valve plate to regulate flow of power fluidthrough said passage to said power cylinder, rear exhaust port means insaid body communicating with the rear portion of said power cylinder,means forming an exhaust passage seat eflective with said supply valveplate to open and close said rear exhaust port means, means forming avalve chamber contiguous with said valve plate, and means for supplyingpower fluid to said valve chamber to urge said supply valve plate towardsaid supply valve seat.

12. An airless spray gun comprising a spray gun body,

means forming a power cylinder in said body, a power piston located insaid power cylinder, passage means in said spray gun body connected to arear portion of said power cylinder, means for supplying power fluid tosaid passage means, a supply valve plate, means forming a supply valveseat effective with said supply valve plate to regulate flow of powerfluid through said passage to said power cylinder, rear exhaust portmeans in said body communicating with the rear portion of said powercylinder, means to open and close said rear exhaust port means, meansforming a valve chamber contiguous with said valve plate, means forsupplying power fluid to said valve chamber during a power stroke ofsaid piston to urge said valve plate toward said supply valve seat whenthe power stroke is completed and for bleeding power fluid from saidvalve chamber during a return stroke of said piston to substantiallyeliminate the urging force by the time the piston has completed thereturn stroke.

i3. An airless spray gun comprising a spray gun body, means forming apower cylinder in said body, a power piston located insaid powercylinder, passage means in said spray gun body connected to a rearportion of said power cylinder, means for supplying power fluid to saidpassage means, fluid valve means to regulate flow of power fluid throughsaid passage to said power cylinder, rear exhaust port means in saidbody communicating with the rear portion of said power cylinder, exhaustvalve means carried by said power piston for opening and closing saidrear exhaust port means, and a spring acting on said piston to move saidpiston toward the rear of said power cylinder when said rear exhaustport means are opened.

References Cited by the Examiner UNITED STATES PATENTS 1,604,043 10/26Hansen 9l240 1,852,591 4/32 Smith, et a1. 913l7 1,949,497 3/34 Stafford,et a1 222334 1,965,038 7/34 Hartman 222334 2,540,357 2/51 Stanley239-329 2,941,726 6/60 Szczepanski 239329 3,018,968 1/62 Levey 2393293,061,202 10/62 Tyler 239-330 3,120,347 2/64 Duke 239332 EVERETT W.KIRBY, Primary Examiner.

1. AN AIRLESS SPRAY GUN COMPRISING A SPRAY GUN BODY, MEANS FORMING APOWER CYLINDER, A POWER PISTON LOCATED IN SAID POWER CYLINDER, PASSAGEMEANS IN SAID SPRAY GUN BODY CONNECTED TO A REAR PORTION OF SAID POWERCYLINDER, MEANS FOR SUPPLYING POWER FLUID TO SAID PASSAGE MEANS, FLUIDVALVE MEANS TO REGULATE FLOW OF POWER FLUID TO SAID POWER CYLINDER, REAREXHAUST PORT MEANS IN SAID BODY COMMUNICATING WITH THE REAR PORTION OFSAID POWER CYLINDER, EXHAUST VALVE MEANS FOR OPENING AND CLOSING SAIDREAR EXHAUST PORT MEANS, AND ADDITIONAL EXHAUST MEANS FOR THE REARPORTION OF SAID POWER CYLINDER AND OPENED WHEN SAID POWER PISTON TRAVELSFORWARDLY A PREDETERMINED DISTANCE IN SAID POWER CYLINDER.